The RAF fighter jets took to the skies to investigate five unidentified aircraft flying in international airspace along the northern and western borders of Estonia, the ministry said in a statement on May 17.

The RAF jets, which have been deployed in Estonia since April, initially shadowed two Su-27 Flanker fighters and an IL-20 'Coot-A' Reconnaissance aircraft to the north of Estonia when two more Su-27 Flankers were detected and intercepted. The Russian military aircraft were operating without transmitting recognized identification codes nor were they communicating with regional air traffic control centers.

'For the second time in a week, the RAF have been on hand to respond to Russian activity at a moment's notice. 24 hours a day, seven days a week, we will continue to secure the Baltic skies on behalf of NATO and our allies,'Defense Secretary Michael Fallon said.

This is the third consecutive year in which the UK has committed to the Baltic Air Policing Mission, the latest rotation sees four RAF Typhoon and pilots from II (Army Co-operation) Squadron from Royal Air Force Lossiemouth deployed to Amari Air Base in Estonia. The RAF Typhoon Sqn, which will remain on BAP until the end of August, is operating alongside Portuguese F-16s based in Siauliai in Lithuania.